1. Field of the Invention
In the case of injectors for injecting highly pressurized fuel into combustion chambers of internal combustion engines, control elements are generally used that contain multiple stepped pistons. In these configurations, the control surface is always larger than the valve seat at which a valve chamber is sealed off from the nozzle inlet of the injection nozzle. The processing of control element pistons embodied as stepped is always laborious and therefore cost-intensive. It is difficult to achieve the exact coaxial embodiment of stepped surfaces partly used as sealing seats.
2. Description of the Prior Art
DE 37 28 817 C2 relates to a fuel injection pump for an internal combustion engine. A control valve member is comprised of a valve shaft, which constitutes a guide bush and slides in a channel, and a valve head, which is connected to the valve shaft and is oriented toward an actuation device. The valve surface of the valve head cooperates with the surface of the control bore forming the valve seat. The valve shaft has a recess on its circumference whose axial span extends from the inlet of the fuel supply line to the beginning of the sealing surface which is disposed on the valve head and cooperates with the valve seat. In the recess, a surface is embodied which is subjected to the pressure of the fuel supply line and whose surface area is equal to that of a surface of the valve head that is subjected to the pressure of the fuel supply line when the control valve is closed. As a result, the valve is pressure-compensated when it is closed. The guide bush contains a spring that loads the control valve in the direction of its open position. In this embodiment, many parts are required for controlling the control valve, which parts move in relation to one another and must move in relation to one another with a high degree of precision.
In the embodiment of a control element as a valve that is struck by the flow centrally, which is proposed according to the invention, a particularly simple embodiment can be achieved. The processing of a one-piece valve extending essentially in the vertical direction is very simple to achieve from a production technology standpoint. The control valve can, for example, be provided with a central through bore whose end nearest the control chamber has an inlet throttle to the control chamber embodied in it. It is also possible to embody a leakage oil control groove on the circumference of the control element, which is struck by the flow centrally, with the leakage oil control groove running essentially in the circumferential direction. An end face of the leakage oil control groove embodied on the control element on the leakage oil side can be embodied as a control surface with a larger diameter compared to the diameter of the control element, which is subjected to the prevailing pressure from the high-pressure accumulation chamber. Consequently, a one-piece control element which is essentially embodied as a turned part on its outer surface and as a drilled part on the inside can reduce the number of working steps required for its manufacture. Through advantageous disposition and utilization of the leakage oil control groove as a control surface for the closing during the closing process of the valve, in a hollow annular chamber encompassing the one-piece control element, it is possible on the one hand to dispose the nozzle discharge at the closing of the valve, and it is possible on the other hand to provide the leakage oil discharge line at the opposite end of the annular chamber.
The control chamber, which can be simply embodied at the upper end of the control element, can be actuated by way of a separately actuatable closing element and is defined by an end face of the control element containing the inlet throttle and is otherwise defined by the walls of the injector housing.
On the lower end of the control element, which can be produced in a very light-weight and simple fashion from a production technology standpoint, a conically configured valve seat is embodied, which can be struck centrally by the flow from the high-pressure accumulation chamber. The valve chamber, which is defined on one side by a correspondingly rounded housing wall and on the other side by a conically configured outer surface of the control element, empties into a nozzle inlet by way of a transverse bore. Originating from the high pressure accumulation chamber inlet by way of the nozzle inlet, a nozzle chamber encompassing a nozzle needle can be loaded with fuel that is under extremely high pressure.
If the control element is embodied of one piece, on the one hand, the leakage oil chamber provided downstream can provide for a rapid discharge of the nozzle inlet and on the other hand, the control surface is embodied in the vicinity of the leakage oil control chamber, which permits a rapid closing of the valve while, at the same time, relieving the pressure of the nozzle inlet. In an advantageous embodiment of the concept underlying the invention, this control surface can be embodied as a simple collar with a leakage oil control groove of a corresponding length extending on it in the axial direction toward the control chamber.
Besides a through bore being provided in a one-piece control element and extending coaxially to the symmetrical line of the control part, this through bore can also be shifted into the injector housing. If the through bore, on whose end an inlet throttle into the control chamber can be provided, is embodied in the injector housing, the control element can be produced from two separate parts. The production of the control element from two valve bodies resting against each other offers advantages from a production technology standpoint with regard to material selection because only the part of the valve body oriented toward the high-pressure accumulation chamber inlet needs to be made of high-strength material. The valve body provided on the downstream end can comprised of material which is easier to process and less expensive. The embodiment of the control element in two separate valve bodies that are independent of each other offers the advantage of greater ease in manufacturing due to the fact that standardized production processes can be performed on numerically controlled processing machines and the valve bodies have a geometry with a low level of complexity that is suitable for numerically controlled processing machines.